Secondary menu

This week's DSP seminar will be a double bill presented by Nicholas J. Bryan, a CCRMA Ph.D. candidate, discussing room impulse response processing, and Keun Sup Lee, a CCRMA visiting scholar, describing recent work on the switched convolution reverberator. The seminar will take place in the CCRMA classroom (Knoll 217) at 3:15 PM this Friday, October 15. Abstracts follow:

Methods for Extending Room Impulse Responses Beyond Their Noise Floor

Nicholas Bryan

Two methods of extending measured room impulse responses below their noise floor and beyond their measured duration are presented. Both methods extract frequency-dependent reverberation energy decay rates, equalization levels, and noise floor levels, and subsequently extrapolate the reverberation decay towards silence. The first method crossfades impulse response frequency bands with a late-field response synthesized from Gaussian noise. The second method imposes the desired decay rates on the original impulse response bands. Both methods maintain an identical impulse response prior to the noise floor arrival in each band and seamlessly transition to a natural sounding decay after the noise floor arrival.

An efficient reverberator structure is proposed for approximating measured reverberation. A fixed convolution matching the early portion of a measured impulse response is crossfaded with a switched convolution reverberator drawing its switched convolution section from the late-field of the measured impulse response. In this way, the early portion of the measured impulse response is precisely reproduced, and the late-field equalization and decay rates efficiently approximated. To use segments of the measured impulse response, the switched convolution structure is modified to include a normalization filter to account for the decay of the late-field between the nominal fixed/switched crossfade time and the time of the selected segment. Further, the measured impulse response late-field is extended below its noise floor in anticipation of the normalization. This structure provides psychoacoustically accurate synthesis of the measured impulse response using less than half a second of convolution, irrespective of the length of the measured impulse response. In addition, the structure provides direct control over the equalization and late-field frequency dependent decay rate. Emulations of EMT 140 plate reverberator and marble lobby impulse responses are presented.